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Rigor mortis and Rigor mortis and

Fish SpoilageFish Spoilage

Dr. Dr. SubhenduSubhendu DattaDatta

Sr. Scientist Sr. Scientist

CIFE, Kolkata Centre, IndiaCIFE, Kolkata Centre, India

What is What is Rigor mortisRigor mortis

Rigor mortisRigor mortis is one of the recognizable is one of the recognizable

signs of death (Latin signs of death (Latin morsmors, mortis, mortis) that is ) that is

caused by a chemical change in the caused by a chemical change in the

muscles after death, causing the limbs of muscles after death, causing the limbs of

the "Cadaver" to become stiff (Latin the "Cadaver" to become stiff (Latin rigorrigor) )

and difficult to move or manipulate and difficult to move or manipulate

A cadaver or corpse is a dead body. A cadaver or corpse is a dead body.

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IntroductionIntroduction

General composition of fish is given below General composition of fish is given below

though there are wide variations from though there are wide variations from

species to species and from fish to fish;species to species and from fish to fish;

Water:Water: 6565--80%80%

Protein:Protein: 12 12 –– 22%22%

Lipids:Lipids: 0.5 0.5 –– 16%16%

Minerals:Minerals: 0.1 0.1 –– 3% 3%

Fishes are perishable commodities. After the catch when fish dieFishes are perishable commodities. After the catch when fish dies the s the biochemical changes responsible for anabolism stop and as inevitbiochemical changes responsible for anabolism stop and as inevitable able consequence only catabolism processes keep functioning.consequence only catabolism processes keep functioning.

The digestive enzymes still being active, instead of acting on fThe digestive enzymes still being active, instead of acting on food ood eaten begin to digest fish tissue components itself. eaten begin to digest fish tissue components itself.

Due to this, fish tissue components e.g. lipids, carbohydrates aDue to this, fish tissue components e.g. lipids, carbohydrates and nd proteins breaks down (autolysis). proteins breaks down (autolysis).

In addition to this, the native bacteria present in the fish mulIn addition to this, the native bacteria present in the fish multiply rapidly tiply rapidly and secrets various enzymes causing rapid breakdown of fish tissand secrets various enzymes causing rapid breakdown of fish tissues. ues.

Lipid oxidation causes rancidity of fish flesh which produces foLipid oxidation causes rancidity of fish flesh which produces foul smell. ul smell.

Autolysis also causes fading of fish pigments, development of ofAutolysis also causes fading of fish pigments, development of off f flavour and browning. flavour and browning.

The rapid colonization and multiplication of bacteria and severaThe rapid colonization and multiplication of bacteria and several other l other autolyticautolytic changes eventually complete the total breakdown of fish changes eventually complete the total breakdown of fish muscle.muscle.

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CHANGES IN FISH FLESH BIOCHEMISTRY CHANGES IN FISH FLESH BIOCHEMISTRY

POST MORTEMPOST MORTEM

The demise of a fish begins a series of irreversible The demise of a fish begins a series of irreversible

changes which lead to spoilage and loss of quality. changes which lead to spoilage and loss of quality.

The natural process The natural process

Slime secretionSlime secretion-- Rigor mortis Rigor mortis →→ DesolutionDesolution of rigor of rigor →→

Autolysis Autolysis

can be slowed down if correct handling and storage can be slowed down if correct handling and storage

procedures are followed.procedures are followed.

On the death of the fish, processes of physical and On the death of the fish, processes of physical and chemical change caused by enzymes and microchemical change caused by enzymes and micro--organisms begin to occur. The complete decay of the fish organisms begin to occur. The complete decay of the fish is the final result of those changes.is the final result of those changes.

PostPost--mortem changes which take place in fish tissue mortem changes which take place in fish tissue occur in the following phases:occur in the following phases:

-- slime secretion on the surface of fishslime secretion on the surface of fish

-- rigor mortisrigor mortis

-- autolysis as enzymatic decomposition of tissuesautolysis as enzymatic decomposition of tissues

-- microbiological spoilagemicrobiological spoilage

The duration of each phase can change or phases can The duration of each phase can change or phases can overlap. This depends on storage conditions, especially overlap. This depends on storage conditions, especially the the temperature temperature which greatly influences these which greatly influences these processes.processes.

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Slime SecretionSlime Secretion

Slime is formed in certain cells of fish skin and the process beSlime is formed in certain cells of fish skin and the process becomes comes very active just after fish death. Some of the fish, for examplevery active just after fish death. Some of the fish, for example eel, eel, secrete more slime than, for comparison, secrete more slime than, for comparison, SalmonidaeSalmonidae and perch. and perch.

Fish which secrete great quantities of slime have poorly developFish which secrete great quantities of slime have poorly developed ed scales; very often the quantity of slime reaches 2scales; very often the quantity of slime reaches 2--3% of the fish 3% of the fish mass and that in turn creates problems during processing. mass and that in turn creates problems during processing.

The secretion process stops with the onset of The secretion process stops with the onset of rigor mortisrigor mortis..

Slime contains large amounts of nitrogenous compounds and these Slime contains large amounts of nitrogenous compounds and these provide good nourishment for microprovide good nourishment for micro--organisms originating from the organisms originating from the environment. environment.

Therefore, the slime spoils quickly: first giving an unpleasant Therefore, the slime spoils quickly: first giving an unpleasant smell smell to the fish, and second opening the way for further and deeper to the fish, and second opening the way for further and deeper bacterial penetration into the fish.bacterial penetration into the fish.

PrePre--rigor conditionrigor condition

One of the important factors determining the spoilage in freshlyOne of the important factors determining the spoilage in freshlycaught fish is caught fish is rigor mortisrigor mortis –– the stiffening of the body. Usually this the stiffening of the body. Usually this develops within 1 develops within 1 –– 7 hrs after death. 7 hrs after death.

As long as the fish is alive, itAs long as the fish is alive, it’’s circulatory system function even after s circulatory system function even after capture. capture.

After death, respiration in organisms ceases to occur, depletingAfter death, respiration in organisms ceases to occur, depleting the the corpse of oxygen used in the making of ATP. One of the corpse of oxygen used in the making of ATP. One of the consequences of the stoppage of the circulatory system is cessatconsequences of the stoppage of the circulatory system is cessation ion of oxygen supply after death. of oxygen supply after death.

But the oxygenated glycogen rich muscle can remain metabolicallyBut the oxygenated glycogen rich muscle can remain metabolicallyactive for hours in preactive for hours in pre--rigor condition. rigor condition.

In the living tissues aerobic breakdown of the glucose is normalIn the living tissues aerobic breakdown of the glucose is normalreaction that takes place in every molecule of glucose oxidized reaction that takes place in every molecule of glucose oxidized results results in the synthesis of 36 molecules of ATP. in the synthesis of 36 molecules of ATP.

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However, after death, anaerobic breakdown of However, after death, anaerobic breakdown of glucose takes place. glucose takes place.

The synthesis of ATP stops and hydrolysis The synthesis of ATP stops and hydrolysis begins as per the reaction given below:begins as per the reaction given below:

ATPaseATPase

ATP ATP ADP+PiADP+Pi …………………… (i)(i)

Rapid decrease in the ATP level and increase Rapid decrease in the ATP level and increase concentration of phosphoric acid are observed. concentration of phosphoric acid are observed.

�� Although certain amount of ATP is synthesized Although certain amount of ATP is synthesized by the hydrolysis of by the hydrolysis of creatinecreatine phosphate by the phosphate by the enzyme enzyme creatinecreatine kinasekinase by the following reaction;by the following reaction;

CrPCrP + ADP Cr + ATP+ ADP Cr + ATP…………………… (ii)(ii)

�� But the But the creatinecreatine reserves in the tissues are not reserves in the tissues are not infinite and soon get exhausted. infinite and soon get exhausted.

�� The small rate ATP synthesis by reaction (ii) can The small rate ATP synthesis by reaction (ii) can no longer compete with the reaction (i) and ATP no longer compete with the reaction (i) and ATP concentration begins to fall to near zero. concentration begins to fall to near zero.

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The concentration of lactic acid formed due The concentration of lactic acid formed due breakdown of glucose is found to be dependent on breakdown of glucose is found to be dependent on the glycogen reserves of the muscle prior to death. the glycogen reserves of the muscle prior to death.

The glycogen reserve of the muscle is directly The glycogen reserve of the muscle is directly related to the struggle the fish has undergone prior related to the struggle the fish has undergone prior to capture and death. to capture and death.

The greater the struggle the fish has experienced The greater the struggle the fish has experienced the lesser are its glycogen reserves and the onset the lesser are its glycogen reserves and the onset of of rigor mortisrigor mortis becomes rapid. becomes rapid.

Therefore,Therefore, Rigor mortisRigor mortis proceeds very quickly in proceeds very quickly in very active fish but rather slowly in inert fish. very active fish but rather slowly in inert fish.

One consequence of the accumulation of lactic acid in One consequence of the accumulation of lactic acid in the muscle is the lowering of pH from near neutrality (pH the muscle is the lowering of pH from near neutrality (pH 7.0) to the lactic acid range (pH 6.0). 7.0) to the lactic acid range (pH 6.0).

The decline of pH affects the quality of the fish tissues, in The decline of pH affects the quality of the fish tissues, in that flesh become firmer and tendency to drip enhances.that flesh become firmer and tendency to drip enhances.

During the initial stages of disappearance of ATP, some During the initial stages of disappearance of ATP, some major protein changes take place. major protein changes take place.

At this stage thick and thin filaments of At this stage thick and thin filaments of myofibrillarmyofibrillarproteins are free to slide past each other. proteins are free to slide past each other.

This indicates that muscles are extensible and can This indicates that muscles are extensible and can contract on stimulation.contract on stimulation.

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Rigor mortis Rigor mortis conditioncondition

At the final phase of ATP breakdown myosin cross At the final phase of ATP breakdown myosin cross bridges interaction are established firmly between the bridges interaction are established firmly between the thick and thin filaments thereby making it nonthick and thin filaments thereby making it non--extensible extensible and hence nonand hence non--contractile.contractile.

Finally the breakdown of ATP becomes complete and Finally the breakdown of ATP becomes complete and the muscle is said to have entered the stage of the muscle is said to have entered the stage of rigor rigor mortismortis. .

This is elaborated more clearly in next few slides with This is elaborated more clearly in next few slides with help of diagrams.help of diagrams.

Muscle consists of several proteins actively involved in Muscle consists of several proteins actively involved in contraction.contraction.

The two major proteins, The two major proteins, actinactin and and myosinmyosin, combine in , combine in the presence of the presence of calcium ionscalcium ions to form to form actomyosinactomyosin. .

ATP then supplies the energy for contraction, and later ATP then supplies the energy for contraction, and later also the energy for the removal of the calcium ions via a also the energy for the removal of the calcium ions via a calcium pump. calcium pump.

This breaks the This breaks the actomyosinactomyosin complex, leaving the complex, leaving the muscle ready for a further contraction.muscle ready for a further contraction.

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Fig 1. Muscle contraction Reaction

On death, the circulatory system stops and the ATP On death, the circulatory system stops and the ATP levels drop. levels drop.

Calcium ions leak, forming Calcium ions leak, forming actomyosinactomyosin. .

However, there is insufficient ATP for the calcium However, there is insufficient ATP for the calcium pump to operate, and so the pump to operate, and so the actomyosinactomyosin complex complex remains unbroken.remains unbroken.

The muscle is now in a continual state of rigidness, The muscle is now in a continual state of rigidness, known as known as rigor mortisrigor mortis. .

Fish is edible in this condition. Fish is edible in this condition.

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Rigor mortisRigor mortis has many technological consequences. has many technological consequences.

If, for example, the bones were removed prior to If, for example, the bones were removed prior to rigor rigor mortismortis the length of the fillet shortens by 30%. the length of the fillet shortens by 30%.

At the same time, the fillet becomes wider and thicker At the same time, the fillet becomes wider and thicker because its volume does not change. because its volume does not change.

This tightness very often causes the connective tissue of This tightness very often causes the connective tissue of individual individual myomeresmyomeres to break; this process is termed to break; this process is termed "gaping" and results in muscle separation which is "gaping" and results in muscle separation which is considered a quality defect. considered a quality defect.

"Gaping" depends on temperature; the higher the "Gaping" depends on temperature; the higher the temperature of fish at the beginning of the rigor mortis temperature of fish at the beginning of the rigor mortis process the greater the gaping of the muscle.process the greater the gaping of the muscle.

Therefore, during rigor mortis fish temperature should be Therefore, during rigor mortis fish temperature should be as low as possible. as low as possible.

For example, for roach and perch kept at 0For example, for roach and perch kept at 0°°C, C, rigor mortis rigor mortis begins 24 hours after death and lasts for 72begins 24 hours after death and lasts for 72--80 hours. 80 hours.

When the same species is kept at 35When the same species is kept at 35°°C it begins 20C it begins 20--30 30 minutes after death and stops after about 3 hours. minutes after death and stops after about 3 hours.

The time The time rigor mortisrigor mortis begins and its duration depend on begins and its duration depend on the the fish speciesfish species (e.g., for carp at 0(e.g., for carp at 0°°C it starts after 48 C it starts after 48 hours, for roach and perch at 0hours, for roach and perch at 0°°C after 24 hours), on the C after 24 hours), on the fish catching techniquefish catching technique, and on , and on fish temperaturefish temperature. .

It was also found that fast swimmers, for example trout, It was also found that fast swimmers, for example trout, undergo undergo rigor mortis rigor mortis faster but for a shorter duration than faster but for a shorter duration than slow swimmers like carp.slow swimmers like carp.

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In those fish which are in good condition (wellIn those fish which are in good condition (well--nourished) nourished) rigor mortisrigor mortis is more is more intensive. Fish put to death just after removal from the water rintensive. Fish put to death just after removal from the water reach a state of each a state of rigor mortisrigor mortis later than those fish which died after a long agony. later than those fish which died after a long agony.

In the case of carp put to death just after capture In the case of carp put to death just after capture rigor mortisrigor mortis begins after 48 begins after 48 hours, but if the carp died after a long agony it sets in after hours, but if the carp died after a long agony it sets in after 24 hours (at 024 hours (at 0°°C).C).

Unnecessary and rough handling of the fish can shorten the time Unnecessary and rough handling of the fish can shorten the time of occurrence of occurrence and duration of and duration of rigor mortisrigor mortis. Such treatment causes stress in live fish.. Such treatment causes stress in live fish.

Fish body temperature is a decisive factor in the onset and duraFish body temperature is a decisive factor in the onset and duration of the tion of the rigor rigor mortismortis process. process.

The higher the temperature the sooner it begins and the faster iThe higher the temperature the sooner it begins and the faster it ceases. This is t ceases. This is evidenced by enzymatic reactions whose speed increases with increvidenced by enzymatic reactions whose speed increases with increased eased temperature. temperature.

At high temperatures it results in greater changes in proteins, At high temperatures it results in greater changes in proteins, the latter causing the latter causing higher loss of tissue juices, e.g., during processing. Usually, higher loss of tissue juices, e.g., during processing. Usually, the later the later rigor rigor mortismortis begins and the longer it lasts, the longer are the storage lifebegins and the longer it lasts, the longer are the storage life of the fish of the fish and its use for consumption.and its use for consumption.

PostPost--rigor conditionrigor condition

Fish spoilage begins due to two causes, autolysis (digestionFish spoilage begins due to two causes, autolysis (digestion of fish muscle of fish muscle and fat by tissue enzymes) and bacterial growth. and fat by tissue enzymes) and bacterial growth.

Autolysis:Autolysis:Autolysis:Autolysis:Autolysis:Autolysis:Autolysis:Autolysis:

The decomposition of the fish occurs as its constituent compoundThe decomposition of the fish occurs as its constituent compounds break s break down. down.

The The proteins, nucleotides and sugars break downproteins, nucleotides and sugars break down, bases are released, , bases are released, the pH falls and the the pH falls and the fats are oxidizedfats are oxidized. These make the fish smelly, rancid . These make the fish smelly, rancid and tough. and tough.

Enzymes in the flesh and gut previously involved in metabolism nEnzymes in the flesh and gut previously involved in metabolism now ow catalysecatalyse autolyticautolytic reactions, in which various compounds decompose. reactions, in which various compounds decompose.

Enzymes in the flesh break down desirable compoundsEnzymes in the flesh break down desirable compounds into tasteless or into tasteless or bitter ones, whilst bitter ones, whilst gut enzymes attack the internal organsgut enzymes attack the internal organs, turning them , turning them into a soupy mess and allowing bacteria to enter the flesh.into a soupy mess and allowing bacteria to enter the flesh.

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Bacterial attackBacterial attack

In a living fish, In a living fish, bacteria are present in the gut and skinbacteria are present in the gut and skin, , but the flesh, which they are prevented from entering, but the flesh, which they are prevented from entering, remains sterile. remains sterile.

Once autolysis begins, however, the bacteria are able to Once autolysis begins, however, the bacteria are able to enter the flesh, whereupon they multiply rapidly and enter the flesh, whereupon they multiply rapidly and decompose the muscle. decompose the muscle.

Anaerobic bacteria (those which operate in the absence Anaerobic bacteria (those which operate in the absence of oxygen) produce a particularly foul type of spoilage of oxygen) produce a particularly foul type of spoilage which results in an inedible fish.which results in an inedible fish.

A number of biochemical changes take place during A number of biochemical changes take place during autolysis, and these are outlined in next few slides.autolysis, and these are outlined in next few slides.

Protein Protein DenaturationDenaturation

DenaturationDenaturation of protein involves the destruction of its of protein involves the destruction of its secondary, tertiary and quaternary structure, reducing the secondary, tertiary and quaternary structure, reducing the protein to a simple polypeptide chain. protein to a simple polypeptide chain.

A number of factors, including slow freezing and variability A number of factors, including slow freezing and variability of storage conditions, cause this of storage conditions, cause this denaturationdenaturation..

A denatured protein has not only lost its ability to function A denatured protein has not only lost its ability to function as an enzyme, but also its "wateras an enzyme, but also its "water--holding" ability.holding" ability.

This results in denatured fish flesh dripping excessively This results in denatured fish flesh dripping excessively when thawed (a situation known as "dripwhen thawed (a situation known as "drip--thaw"), and thaw"), and appearing white, dull and spongy, and upon chewing appearing white, dull and spongy, and upon chewing becoming fibrous and tasteless.becoming fibrous and tasteless.

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Decreasing flesh pHDecreasing flesh pH

A living fish has a flesh pH of 7.0. A living fish has a flesh pH of 7.0.

However, after death residual glycogen is broken down However, after death residual glycogen is broken down via via glycolosisglycolosis to to pyruvicpyruvic acid and then lactic acid. acid and then lactic acid.

Phosphoric acid is produced due to breakdown of ATP.Phosphoric acid is produced due to breakdown of ATP.

As this happens, the flesh becomes more acidic.As this happens, the flesh becomes more acidic.

If the pH remains above 6.6, the texture is reasonably soft, If the pH remains above 6.6, the texture is reasonably soft, but below this level the flesh becomes firm and eventually but below this level the flesh becomes firm and eventually unacceptably tough.unacceptably tough.

TVBTVB--Total Volatile BaseTotal Volatile BaseTVB is a measure of the total amount of a variety of nitrogenTVB is a measure of the total amount of a variety of nitrogen--containing containing substances which are produced during storage. substances which are produced during storage.

An example of a volatile base present in the flesh is a An example of a volatile base present in the flesh is a trimethylaminetrimethylamine (TMA), (TMA), which is formed from the reduction of which is formed from the reduction of trimethylaminetrimethylamine oxide. oxide.

Marine fish contain a small amount of Marine fish contain a small amount of trimethylaminetrimethylamine oxide, the function of oxide, the function of which is unknown. which is unknown.

This This odourlessodourless and tasteless compound is reduced by invading bacteria to and tasteless compound is reduced by invading bacteria to TMA, which is TMA, which is characterisedcharacterised by its "fishy" smell. by its "fishy" smell.

TMA, though, only becomes useful as a quality index during the mTMA, though, only becomes useful as a quality index during the middle and late iddle and late stages of spoilage after the bacteria have invaded the fish. stages of spoilage after the bacteria have invaded the fish.

TrimethylamineTrimethylamine oxide is converted in the muscle tissue into oxide is converted in the muscle tissue into dimethylaminedimethylamine(DMA) and formaldehyde by enzyme action during frozen storage. (DMA) and formaldehyde by enzyme action during frozen storage.

This formaldehyde is able to crosslink with protein, denaturing This formaldehyde is able to crosslink with protein, denaturing the muscle the muscle structure. The fish loses water when it is thawed, and when cookstructure. The fish loses water when it is thawed, and when cooked has a tough ed has a tough and fibrous texture.and fibrous texture.

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LipidLipid Oxidation and HydrolysisOxidation and Hydrolysis

The two major deteriorative changes which occur in fish are:The two major deteriorative changes which occur in fish are:

(i). The enzymatic hydrolysis of lipids (fats) to produce free f(i). The enzymatic hydrolysis of lipids (fats) to produce free fatty acids atty acids

and glycerol:and glycerol:

(ii) the oxidation of fish oils yielding the rancid odours and tastes which are the major problem encountered in fish storage.

Nucleotide BreakdownNucleotide Breakdown

This involves the enzymatic breakdown of This involves the enzymatic breakdown of

the energy carrier ATP, as outlined in the the energy carrier ATP, as outlined in the

next slide next slide ……..

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Thus as spoilage

proceeds the amount of

ATP present decreases,

causing rigor mortis and

post rigor conditions.

Measures to reduce fish spoilage Measures to reduce fish spoilage

during storageduring storage

Fish should be consumed fresh or should be Fish should be consumed fresh or should be properly preserved so that its palatability and properly preserved so that its palatability and nutritive value are not seriously impaired. nutritive value are not seriously impaired.

A substantial percentage (25A substantial percentage (25--30%) of the 30%) of the catches landed at present in India reaches the catches landed at present in India reaches the consumer in subconsumer in sub--standard condition due to standard condition due to unsatisfactory methods employed in catching unsatisfactory methods employed in catching fish, their preservation and transport, and fish, their preservation and transport, and inadequate and insufficient marketing facilities.inadequate and insufficient marketing facilities.

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After bringing to the factory, the fish are washed with After bringing to the factory, the fish are washed with flowing water to remove the heavily contaminated slime. flowing water to remove the heavily contaminated slime.

ShrimShrim contains greater amount of free amino acids than contains greater amount of free amino acids than fish and also highly active fish and also highly active proteolyticproteolytic enzymes.enzymes.

Shrimps are highly susceptible to Shrimps are highly susceptible to melanosismelanosis, a , a characteristic black spot development caused by an characteristic black spot development caused by an enzymatic reaction. enzymatic reaction.

They are highly perishable, and require adequate They are highly perishable, and require adequate refrigeration and expeditious handling to prevent refrigeration and expeditious handling to prevent decomposition.decomposition.

Fish often get contaminated through woodenFish often get contaminated through wooden--boxes, ice, boxes, ice, dressingdressing--tables etc., which usually carry heavy bacterial tables etc., which usually carry heavy bacterial load. load.

Proper treatment of surfaces, equipments etc., with Proper treatment of surfaces, equipments etc., with disinfectants and detergents, and use of potable water for disinfectants and detergents, and use of potable water for washing and icewashing and ice--making are necessary to reduce bacterial making are necessary to reduce bacterial contamination. contamination.

The initial bacterial load and the nature of contaminants The initial bacterial load and the nature of contaminants play a vital role in the deterioration of fish in the later play a vital role in the deterioration of fish in the later stages. stages.

These bacteria are These bacteria are thermophilicthermophilic in nature and grow faster in nature and grow faster with the rise in temperature, thereby produce unpleasant with the rise in temperature, thereby produce unpleasant endend--products.products.

Therefore, the practical way to preserve fish in good Therefore, the practical way to preserve fish in good condition is to store fish at low temperature. condition is to store fish at low temperature.

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HandlingHandling (of Shrimp)(of Shrimp) prior to prior to

preservationpreservation

Shrimp being a highShrimp being a high--value product yielding excellent returns, is well value product yielding excellent returns, is well handled in India. handled in India.

Considerable improvements have been made in loading, washing, Considerable improvements have been made in loading, washing, icing, sorting, grading, beheading, peeling, icing, sorting, grading, beheading, peeling, deveiningdeveining and cooking to and cooking to meet high standards required by importing countries. meet high standards required by importing countries.

The water used for prawn/fish processing factories may have to bThe water used for prawn/fish processing factories may have to be e chlorinated to a residual level of 10 chlorinated to a residual level of 10 ppmppm to get full protectionto get full protection. .

Efficient handling immediately after shrimp harvest is very effeEfficient handling immediately after shrimp harvest is very effective in ctive in preventing black discolouration on raw shrimp. preventing black discolouration on raw shrimp.

TyrosinaseTyrosinase and and polyphenolpolyphenol oxidaseoxidase, that , that catalysecatalyse black spot black spot formation, are present in large quantities in the digestive systformation, are present in large quantities in the digestive system of em of the shrimp. the shrimp.

Removal of heads immediately after the shrimp has been brought, Removal of heads immediately after the shrimp has been brought, followed by thorough washing and chilling with ice blocks removefollowed by thorough washing and chilling with ice blocks removeenzymes and substrates and prevent blackening. enzymes and substrates and prevent blackening.

Improved technology is now available for headless shell on peeleImproved technology is now available for headless shell on peeled, d, peeled and peeled and deveineddeveined, cooked and peeled shrimp, and tall, cooked and peeled shrimp, and tall--onon--round round butterfly style. butterfly style.

When processing butterfly style, each shrimp is split right downWhen processing butterfly style, each shrimp is split right down the the centre, and to the exact depth desired regardless of size variatcentre, and to the exact depth desired regardless of size variations. ions.

The shrimp are peeled and The shrimp are peeled and deveineddeveined individually and gently, so that individually and gently, so that the breakage is minimum possible. the breakage is minimum possible.

The shrimp are washed properly with an abundant flow of potable The shrimp are washed properly with an abundant flow of potable water.water.

While While deveiningdeveining the shrimp should be kept in minimum quantity of the shrimp should be kept in minimum quantity of chilled water to retain its characteristics flavour and colour. chilled water to retain its characteristics flavour and colour.

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PackagingPackaging

Numbers of improvements have been made in the traditional Numbers of improvements have been made in the traditional containers. containers.

A new bamboo containers with polytheneA new bamboo containers with polythene--lined gunny as insulator lined gunny as insulator has proved efficient. has proved efficient.

In consists of outer bamboo basket separated from the inner one In consists of outer bamboo basket separated from the inner one by by polyfilmpolyfilm--lined gunny. lined gunny.

PolyfilmPolyfilm inside the inner basket prevents the wetting of the liner. inside the inner basket prevents the wetting of the liner.

Plastic coated wooden boxes are introduced which can be cleaned Plastic coated wooden boxes are introduced which can be cleaned as as they are less liable to spoilages and bacterial contamination isthey are less liable to spoilages and bacterial contamination isreduced to minimum. reduced to minimum.

Use of disinfectants such as hypochlorite solution and Use of disinfectants such as hypochlorite solution and quarternaryquarternaryammonium compounds and scrubbing of the surfaces of the boxes ammonium compounds and scrubbing of the surfaces of the boxes reduce bacterial loads. reduce bacterial loads.

Bamboo baskets lined with Bamboo baskets lined with bituminbitumin--coated with coated with kraftkraft paper, jute fabric paper, jute fabric

and polythene keep iced fish (1:1) for 18and polythene keep iced fish (1:1) for 18--20 hr in good condition. 20 hr in good condition.

Fish packed in iceFish packed in ice (1:1) in a 2.5 cm thick plywood(1:1) in a 2.5 cm thick plywood--box insulated with box insulated with

thermocolethermocole can remain in satisfactory condition for 55can remain in satisfactory condition for 55--60 hr at 2560 hr at 25--

303000C, and storage life can be doubled when kept at refrigerated C, and storage life can be doubled when kept at refrigerated

temperature (4temperature (4--5500C). C).

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Polyurethane is a better substitute as insulating Polyurethane is a better substitute as insulating material both for expanded polythene and polystyrene. material both for expanded polythene and polystyrene.

Shrimp are usually packed between ice layers in Shrimp are usually packed between ice layers in bamboo baskets, tea chest boxes or boxes of different bamboo baskets, tea chest boxes or boxes of different materials, particularly the high density polythene materials, particularly the high density polythene (HDPE) containers. (HDPE) containers.

The top layers of shrimp baskets are sometimes The top layers of shrimp baskets are sometimes crushed, as baskets are stacked a top each other, use crushed, as baskets are stacked a top each other, use of HDPE containers overcomes this problem.of HDPE containers overcomes this problem.

Vehicles for iced shrimp transportation are now usually Vehicles for iced shrimp transportation are now usually insulated and covered so that they are not exposed to insulated and covered so that they are not exposed to dust, files, sun and wind.dust, files, sun and wind.

TransportationTransportation

Inefficient internal distribution poses several problems in IndiInefficient internal distribution poses several problems in India where a where the consuming centres are very far way from fish landing centresthe consuming centres are very far way from fish landing centres. .

The cold chain distribution system in Karnataka (since 1973) is The cold chain distribution system in Karnataka (since 1973) is an an ideal example of scientific and systematic distribution of frozeideal example of scientific and systematic distribution of frozen fish n fish in the interior parts of our country. in the interior parts of our country.

Thorough improvements in transportation facilities, an organizedThorough improvements in transportation facilities, an organizedtrade has been developed in Gujrat for transporting fresh fish ttrade has been developed in Gujrat for transporting fresh fish to o distant areas in northern India.distant areas in northern India.

Transport of fish by refrigerated vans beyond 600 km is Transport of fish by refrigerated vans beyond 600 km is uneconomical. uneconomical.

Refrigerated rail wagons introduced recently on a few routes Refrigerated rail wagons introduced recently on a few routes transport only 0.06% of the total catch.transport only 0.06% of the total catch.

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Preservation with antibioticsPreservation with antibiotics

Chlortetracycline (CTC at 5 Chlortetracycline (CTC at 5 ppmppm level as CTClevel as CTC--ice) prolongs the shelfice) prolongs the shelf--life of fish life of fish in ordinary ice. in ordinary ice.

The most efficient way of using CTC is to incorporate in water @The most efficient way of using CTC is to incorporate in water @5 5 ppmppm, the ice , the ice so formed is almost indistinguishable from ordinary ice, and at so formed is almost indistinguishable from ordinary ice, and at the same time the same time possesses good possesses good bacteriostaticbacteriostatic properties. properties.

The CTC treatment should start as soon as possible after the fisThe CTC treatment should start as soon as possible after the fish have been h have been captured. captured.

The CTC prolongs the storage life of fresh fish fillets stored aThe CTC prolongs the storage life of fresh fish fillets stored at room t room temperature. temperature.

It is not effective for round and eviscerated fish of larger sizIt is not effective for round and eviscerated fish of larger size as dip treatment, e as dip treatment, probably because the antibiotic cannot penetrate into the muscleprobably because the antibiotic cannot penetrate into the muscle through thick through thick skin and wellskin and well--developed scales and hard thick membrane lining the visceral developed scales and hard thick membrane lining the visceral cavity. cavity.

The CTC when used with refrigerated seaThe CTC when used with refrigerated sea--water extends the storage life of fish water extends the storage life of fish held at held at --101000C in sea water or weak (3%) sodium chloride solution. At presentC in sea water or weak (3%) sodium chloride solution. At present, , in India no antibiotic is employed for fish preservation. in India no antibiotic is employed for fish preservation.

ChillingChilling

Chilling is an effective way of reducing spoilage in fish, if itChilling is an effective way of reducing spoilage in fish, if it is done is done quickly, handled carefully and hygienically. quickly, handled carefully and hygienically.

The object of chilling is to cool the fish as quickly as possiblThe object of chilling is to cool the fish as quickly as possible, to as e, to as low a temperature as possible, without freezing. low a temperature as possible, without freezing.

Chilling cannot prevent spoilage altogether but in general, the Chilling cannot prevent spoilage altogether but in general, the colder colder the fish, the greater the reduction in bacterial and enzyme actithe fish, the greater the reduction in bacterial and enzyme activity. vity.

In order to chill fish they must be surrounded by a medium whichIn order to chill fish they must be surrounded by a medium which is is colder than they are. colder than they are.

The medium could be a liquid, solid or gas but of the possible The medium could be a liquid, solid or gas but of the possible alternatives, ice has much to command it. alternatives, ice has much to command it.

The ratio of ice to fish is roughly 1:1 by weight. If the store The ratio of ice to fish is roughly 1:1 by weight. If the store was was insulated, this ratio could be as low as 1:5. Iceinsulated, this ratio could be as low as 1:5. Ice--storage is relatively storage is relatively shortshort--term method of preservation, with storage lives varying from term method of preservation, with storage lives varying from few days to four weeks. few days to four weeks.

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The length of storage depends on a large number of The length of storage depends on a large number of factors including species, size, method of capture, fat factors including species, size, method of capture, fat content, breeding condition, feeding regime and method content, breeding condition, feeding regime and method of killing. In general terms, during storageof killing. In general terms, during storage

nonnon--fatty (or white fish) keep longer than fatty fish.fatty (or white fish) keep longer than fatty fish.

freshwater fish keep longer than marine fishfreshwater fish keep longer than marine fish

fish from warm waters keep longer than fish from fish from warm waters keep longer than fish from temperate waters. temperate waters.

Higher the temperature of storage, shorter the shelf life of Higher the temperature of storage, shorter the shelf life of fish. fish.

As a general rule, for every hour that the fish are kept at As a general rule, for every hour that the fish are kept at ambient temperature the equivalent of one day's storage ambient temperature the equivalent of one day's storage life is lost and for every 5life is lost and for every 50C and 0C and 00C that they are stored, C that they are stored, the storage life in ice is reduced by half. the storage life in ice is reduced by half.

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FreezingFreezing

One of the best ways to arrest all the biochemical changes and One of the best ways to arrest all the biochemical changes and bacterial growth occurred in post rigor condition is to lower thbacterial growth occurred in post rigor condition is to lower the e temperature of stored fish. temperature of stored fish.

By lowering the temperature fish spoilages can be retarded By lowering the temperature fish spoilages can be retarded considerably but not completely. considerably but not completely.

Freezing is by far the best method of heat removal of fish. The Freezing is by far the best method of heat removal of fish. The faster faster the freezing process, the lesser the spoilage. Therefore, quick the freezing process, the lesser the spoilage. Therefore, quick freezing is adopted commercially. freezing is adopted commercially.

In practice, freezer with an operational temperature of In practice, freezer with an operational temperature of -- 404000C are C are used for freezing of fish. used for freezing of fish.

The recommended level at which the temperature of the fish has tThe recommended level at which the temperature of the fish has to o be brought down is be brought down is --303000C and the interior part of the fish has to be C and the interior part of the fish has to be --202000C. C.

The recommended cold storage temperature is now The recommended cold storage temperature is now -- 30300C. C.

However in tropical countries like India most of the cold storagHowever in tropical countries like India most of the cold storages are es are seen maintained at seen maintained at --2020±±220C. C.

Quick freezing of fish is more desirable than slow freezing. TheQuick freezing of fish is more desirable than slow freezing. The faster faster the freezing process, smaller the size of ice crystals formed bythe freezing process, smaller the size of ice crystals formed byfreezing of water in the fish muscle. freezing of water in the fish muscle.

Small ice crystals scatter light giving a chalky white colour toSmall ice crystals scatter light giving a chalky white colour to the the frozen fish. frozen fish.

Slow freezing results in the formation of larger ice crystals inSlow freezing results in the formation of larger ice crystals in fish fish flesh. flesh.

However, different sizes of ice particles do not affect the qualHowever, different sizes of ice particles do not affect the quality of ity of thawed fish except the texture of fish muscle. thawed fish except the texture of fish muscle.

Freezing by using superFreezing by using super--cooled gases, liquid nitrogen and solid cooled gases, liquid nitrogen and solid carbon dioxide is rapidly gaining momentum in the food industry.carbon dioxide is rapidly gaining momentum in the food industry.Cryogenic freezing is expected to gain considerable importance iCryogenic freezing is expected to gain considerable importance in n India in the near future.India in the near future.

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Freshly processed fish fillets laid out on Freshly processed fish fillets laid out on freezing trays freezing trays

Freezing of fish

CanningCanningCanningCanning is a method of preserving fish in which the fish is processed ais a method of preserving fish in which the fish is processed and nd sealed in an airtight container. sealed in an airtight container.

This and all types of packaging prevent microorganisms from enteThis and all types of packaging prevent microorganisms from entering and ring and proliferating inside.proliferating inside.

In India, canning is done mainly for oilIn India, canning is done mainly for oil--sardine, pomfret. Mackerel, tuna in oil and sardine, pomfret. Mackerel, tuna in oil and shrimp in brine.shrimp in brine.

Canning of shrimp in brine:Canning of shrimp in brine: The freshly caught shrimp are throughly washed with The freshly caught shrimp are throughly washed with water. Soft, discoloured, broken or otherwise defective shrimp awater. Soft, discoloured, broken or otherwise defective shrimp are discarded. re discarded. The shrimp are then beheaded, peeled and deveined. The deveined The shrimp are then beheaded, peeled and deveined. The deveined shrimp shrimp shrimp are blanched in boiling brine (8%) for about 6shrimp are blanched in boiling brine (8%) for about 6--8 minutes depending upon 8 minutes depending upon the size of shrimpp till they curl in ringthe size of shrimpp till they curl in ring--like form. On blanching shrimp assumes like form. On blanching shrimp assumes attractive pink to red colour. After blanching shrimp are driedattractive pink to red colour. After blanching shrimp are dried for a few minutes for a few minutes in air current to dry the surface moisture. The blanched shrimp in air current to dry the surface moisture. The blanched shrimp after grading and after grading and weighing are placed in a lacquered cans of the size 301X206 or 3weighing are placed in a lacquered cans of the size 301X206 or 301X109. Hot 01X109. Hot brine of 1.5brine of 1.5--2.0% strength is added to each can before sealing. The cans are 2.0% strength is added to each can before sealing. The cans are then adequately retorted. After cooling, the cans are suitably lthen adequately retorted. After cooling, the cans are suitably labelled and abelled and packed in attractive cartons.packed in attractive cartons.

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Curing of fishCuring of fish

Fish curing includes methods of curing fish by includes methods of curing fish by dryingdrying, , saltingsalting, , smokingsmoking, , and and pickingpicking, or by combination of these processes have been employed , or by combination of these processes have been employed since ancient times. since ancient times.

All of these techniques are still used today but the more modernAll of these techniques are still used today but the more moderntechniques of freezing and canning have taken on a large importatechniques of freezing and canning have taken on a large importance.nce.

These are low cost processing technique to preserve fish. Small These are low cost processing technique to preserve fish. Small pelagic pelagic fishes can be salted and dried within 2 days, but during inclemefishes can be salted and dried within 2 days, but during inclement weather nt weather the period could extend to 5the period could extend to 5--7 days. 7 days.

This results in poor quality of fish due to harbouring of spoilaThis results in poor quality of fish due to harbouring of spoilage bacteria ge bacteria and insect larvae. and insect larvae.

With With salted fishsalted fish, the moisture content decreases due to osmosis , the moisture content decreases due to osmosis approximately at the inverse rate of salt uptake. approximately at the inverse rate of salt uptake.

This phenomenon is rapid for first 10 hours and stabilized afterThis phenomenon is rapid for first 10 hours and stabilized after that time. that time.

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By salting, the moisture content of fish is brought around 38% wBy salting, the moisture content of fish is brought around 38% when bacterial hen bacterial growth is inhibited. growth is inhibited.

When the moisture content of fish is reduced to 25% When the moisture content of fish is reduced to 25% autolyticautolytic activity is greatly activity is greatly reduced, while mould growth is prevented if moisture level is rereduced, while mould growth is prevented if moisture level is reduced to 15%.duced to 15%.

Fish drying in the sunFish drying in the sun

Salt curing may be dry curing (1 part of salt in every 6 parts oSalt curing may be dry curing (1 part of salt in every 6 parts of gutted fish f gutted fish ––cured in sun) or wet curing (1 parts of salt in every 3 parts ofcured in sun) or wet curing (1 parts of salt in every 3 parts of fish fish –– slated slated fish are left in the tank for about 8 days, then wet salted fishfish are left in the tank for about 8 days, then wet salted fish are marketed are marketed directly). directly).

In a process called In a process called Pit curingPit curing, fish treated with slat are buried in pit. Pit , fish treated with slat are buried in pit. Pit curing requires more salt than any other type of curing. curing requires more salt than any other type of curing.

Smoking of fishSmoking of fish is not practiced in India. is not practiced in India.

Eviscerated and washed fishes are brined in 20% table salt for 1Eviscerated and washed fishes are brined in 20% table salt for 100--20 20 minutes. minutes.

Then subjected to steam cooking and hot smoking for about 3Then subjected to steam cooking and hot smoking for about 3--4 hrs. This 4 hrs. This imparts attractive yellow colour to fish. imparts attractive yellow colour to fish.

The processed product is highly delicious and liked by many. The processed product is highly delicious and liked by many.

The smoked fish packed in coconut leaves can be kept at least foThe smoked fish packed in coconut leaves can be kept at least for 2r 2--3 days 3 days at room temperature (25at room temperature (25--303000C) without spoilage compared to hardly a few C) without spoilage compared to hardly a few hours of storage of the fresh fish. hours of storage of the fresh fish.

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Fish smokingFish smoking

Fish drying in drierFish drying in drier

PicklingPickling

Pickling with salt, vinegar, sugar Pickling with salt, vinegar, sugar and spices is also widely and spices is also widely employed for fish curing. A great employed for fish curing. A great variety of fishery products variety of fishery products prepared with vinegar and prepared with vinegar and spices enjoys wide popularity in spices enjoys wide popularity in India and NorthIndia and North--European European countries.countries.

Although they are semiAlthough they are semi--perishable in nature, they perishable in nature, they possess greater appeal to possess greater appeal to consumers than salted and dried consumers than salted and dried fish. fish.

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and so onand so on…………

Aim of all the processes of fish preservation and Aim of all the processes of fish preservation and

processing is to increase shelf life of fishprocessing is to increase shelf life of fish